Slide fasteners are well known in the art. The usual slide fastener comprises a tape provided with a plurality of metal projections disposed along a longitudinal edge thereof to define interlocking head members. These tapes are paired, wherein each mating tape is secured to an opposite side of an opening in the fabric. A slider is disposed between the tapes and acts to bring both interlocking head members together to form a closure. The above-mentioned slide fasteners are usually expensive to manufacture and are inoperable once one of the metal head members becomes disengaged from the tape.
Other forms of slide fasteners have been attempted. Rather than using a series of metal head members, a continuous coil has been attached to a tape to form a stringer, wherein the coil interlocks with a mating coil secured to anassociated tape. Another form has been to use a continuous wire wherein the wire is bent in a serpentine fashion to define interlocking head members. In the case of both the coil and the serpentine-type wires, the effectiveness of the slide fastener depends upon the skill of the operator joining the coil and serpentine type wires to the tape, wherein such operation is critical. Furthermore, these coils and wires are usually provided with enlarged interlocking head members, wherein it has been found difficult to provide a uniform positioning and sizing of these head members with respect to themselves and to the tape. When these head members are not uniform, the slide fastener has a tendancy to stick or clog or snake, making it very difficult to move the slider to the open and closed positions. From the above, it is seen that securing the coil or wire to the tape becomes a difficult operation in order to obtain a workable slide fastener. Usually a cord is secured to the tape to provide strength for the unit, wherein the cord requires additional time in the securement thereof, and increases the skill required in the operation.
A substantial improvement of the aforementioned examples of the prior art is disclosed in U.S. Pat. Nos. 3,732,601 and 3,770,862, granted to Fred H. Rojahn on May 15, 1973 and Nov. 6, 1973, respectively. In these prior U.S. patents an improved stringer blank and method for making same are disclosed.
The stringer blank disclosed in U.S. Pat. No. 3,732,601 comprises an elongated body having a pair of outwardly extending guide rib-like members that are disposed on one face thereof. The guide rib-like members are transversely spaced apart and are disposed adjacent the longitudinal edge portions of the body. First and second sets of a plurality of longitudinally, equally spaced apart slots are provided on the body with the slots extending from one longitudinal edge portion of the body to a transversely opposite, longitudinal edge portion in order to define a series of transverse, substantially parallel ladder-like ribs wherein each of the ribs is provided with a centrally located enlarged portion and a transversely spaced apart pair of abutment members that are disposed on opposite faces of the body between the pair of guide rib-like members. The first set of slots extend through one longitudinal edge portion of the body and are open on one end thereof. The second set of slots extend through the transversely opposite longitudinal edge portion of the body and is open on an opposite end thereof with the first set of slots being alternately disposed with respect to the second set of slots.
The stringer blank disclosed in the aforementioned issued U.S. Patents may be made of a heat resistant plastic material. The enlarged portion described hereinabove may also include an outwardly extending element and a recess disposed on each side of the element adjacent its base portion.
The aforementioned U.S. patents also teach a method of forming the stringer blank disclosed therein. The method taught by the U.S. patents include the steps of extruding a longitudinally extending body and simultaneously extruding a pair of outwardly longitudinally extending guide rib-like members on one side of the body as well as a pair of longitudinally extending abutment members on the opposite side of the body. The patented method also includes the step of positioning the guide rib-like members, during extrusion, in a transversely spaced apart position with each guide rib-like member being formed adjacent a longitudinal edge portion of the body. Transverse slots are then cut in the body to form a blank having a plurality of longitudinally, equally spaced apart slots that provide a series of transverse, substantially parallel ladder-like ribs.
The above method also includes the steps of providing a centrally located, enlarged portion and a transversely spaced apart pair of abutment members on each ladder-like rib and then simultaneously cutting one longitudinal edge portion and one guide rib-like member when transversely cutting a first set of the spaced slots to extend the first set of spaced slots through one longitudinal edge portion of the blank in order to provide an opening on one end of each slot of the first set. The other longitudinal edge portion and other guide rib-like member is simultaneously cut when transversely cutting a second set of spaced slots to extend the second set through the other longitudinal edge of the blank in order to order to provide an opening on an opposite end of each slot of the second set. The slots of the first set are alternately positioned with respect to the slots of the second set in order to provide alternating openings in the longitudinal edges of the body. Accordingly, the blank is then folded in half lengthwise and the pair of abutment members on each rib are abutted to form U-shaped projection elements each having the enlarged portion at its free end thereof and in order to define an open fabric receiving slot at an opposite end thereof.